1. Field of the Invention
This invention relates to a battery sealing structure with an explosion-proof function of preventing-battery explosion due to an abnormal increase of the inner pressure in the battery and, more particularly, to a battery sealing structure, which is capable of excellently sealing the battery and can contribute to improvements in battery assembling operation efficiency.
2. Prior Art
Recently, small-size portable electronic devices such as cellular phones, portable note personal computers, video cameras, etc. have remarkably spread. These devices extensively use small-size, high capacity lithium ion secondary batteries.
When such a lithium ion secondary battery is short-circuited or overcharged due to causes such as a trouble in the apparatus in which the battery is used or an erroneous use thereof, the temperature is increased, and also gas may be generated in the battery to increase the pressure in the battery. To prevent excessive current in the battery, a safety valve having an explosion-proof function and PTC (Positive Temperature Coefficient) element with the resistance thereof having a positive temperature coefficient are provided in the battery.
The safety valve and the PTC element are accommodated together with a cap member which serves as an external electrode terminal of the battery, and a stripper member which is deformed to cut current between the safety valve and a lead as a result of an increase of the inner pressure in the battery, in a substantially cylindrical seal member which seals the accommodated components while insulting the components from the battery housing. The accommodated components are engaged with one another in an overlapped fashion in the seal member. In this state, they are set in an opening of the battery housing, and caulked by a press means to seal the battery.
In the above prior art battery sealing structure, however, it is very difficult to completely seal the overlapped metal portion of the cap member, PTC element and safety valve. In the lithium ion secondary battery, therefore, the electrolyte may leak out under severe conditions. Accordingly, in the prior art battery, seal rubber coating is used to seal overlapped metal portions of the cap member, the PTC element and the safety valve.
However, the operations of providing the seal rubber coating over the overlapped metal portions of the cap member, PTC element and safety valve, are unsuitable for a flow operation. Besides, the components are engaged together less tightly and are more readily separable from one another in correspondence to the thickness of the seal rubber coating. This is undesirable for robots and parts feeders which are needed for mass production by a consistent flow operation.